1. Field of the Invention
The present invention relates to a sensor for measuring the fill level in a container. More particularly, the present invention provides a parabolic antenna with a sub reflector integrated into the radome.
2. Description of the Related Art
Sensors designed for measuring the fill level in a container that is filled with a liquid or with bulk material by determining the delay time of high-frequency signals are known in the art, wherein the sensor is embodied as a parabolic antenna which comprises a main reflector, a sub reflector, and a hollow waveguide, which is connected to the main reflector and which is oriented with its front end toward the sub reflector for coupling electromagnetic waves in and/or out.
Parabolic antennas embodied as sensors can therefore be used for measuring the fill level of liquids or for measuring the fill level of bulk material or for determining the level of liquids or bulk material. Sensors of this type are frequently required to withstand high pressures or high temperatures, and frequently are used in environments that contain aggressive media. To protect their components against corrosion and destruction, most such sensors are therefore equipped with a protective shell or a radome.
In the measurement of fill levels by determining delay times of high-frequency signals, high-frequency pulses are transmitted via an antenna and are reflected on the surface of a medium. The reflected high-frequency pulses are then received by the sensor. From the time difference between transmission of the high-frequency pulse and reception of the reflected high-frequency pulse, the distance of the sensor from the surface of the respective medium can be determined. Fill level measuring devices embodied as parabolic antennas for monitoring and determining fill levels in a container are known in the prior art.
DE 10 2009 000 733, for example, the entire contents of which are incorporated herein by reference, discloses a fill level measuring device, which has a special temperature and a hermetic seal that is stable under pressure. In this case, a process separation unit is proposed, which is equipped at least with a radiation structure that is transparent to high-frequency signals, a retention clip, and a coupling sleeve, wherein the radiation structure encompasses the hollow waveguide flush in a predefined region on the exterior side of the hollow waveguide, and wherein a radial enclosure of the region of the radiation structure that encompasses the hollow waveguide is embodied as a mounted coupling sleeve. The radiation structure is thereby pressed in a positive connection against the exterior of the hollow waveguide, forming a tight seal, and the metallic retention clip is preferably attached to the metallic sub reflector and to the mounted metallic coupling sleeve. However, part of the electromagnetic wave exiting the waveguide is reflected and deflected by this retention clip, so that the emitted electromagnetic radiation field is disrupted. However, during measurement, such undesirable reflections lead to an objectionable reduction in the signal-to-noise ratio, which can in some cases be substantial, and which can cause the echo to disappear into noise, making measurement of the fill level impossible.
DE 10 2005 049 242, for example, the entire contents of which are also incorporated herein by reference, attempts to solve this problem by employing a diffusion disk for removing the interfering portion of the electromagnetic waves laterally, past the exciter. In this process, the electromagnetic waves transmitted by the exciter are concentrated only partly by the parabolic mirror and radiated to the bulk material. The other part of the electromagnetic waves transmitted by the exciter is not concentrated, and is instead removed laterally by the diffusion disk. In this manner, the signal-to-noise ratio can be improved particularly in the short range, and the quality and sensitivity of measurement can be increased. The diffusion disk is arranged at the center of the parabolic mirror. In the embodiment examples of DE 10 2005 049 242, the exciter is coupled directly to the hollow waveguide and securely connected thereto, and is optionally protected by a radome. However, this device has the disadvantage that, on one hand, only part of the electromagnetic radiation is available for measuring the fill level, and on the other hand, by mounting the exciter with the hollow waveguide, additional interference with the electromagnetic field can occur.
The present invention therefore addresses the problem of providing a sensor for a fill level measuring device, which has no elements that interfere with the antenna array of the sensor, but which at the same time is easy to handle.
Accordingly, there is a need for an improved sensor, method of providing a sensor and a desire to overcome at least one of the detriments noted above.